Audio recording and reproduction has in recent years progressed from monaural single-channel format to dual-channel stereo format and more recently to multi-channel format, for example five-channel audio format as often used in home movie systems. The introduction of super audio compact disks (SACD) and digital video disc (DVD) data carriers has resulted in such five-channel audio reproduction contemporarily gaining interest. Many users presently own equipment capable of providing five-channel audio playback in their homes; correspondingly, five-channel audio programme content on suitable data carriers is becoming increasingly available, for example the aforementioned SACD and DVD types of data carriers. On account of growing interest in multi-channel programme content, more efficient coding of multi-channel audio programme content is becoming an important issue, for example to provide one or more of enhanced quality, longer playing time and even more channels. Moreover, this growing interest has prompted standardization bodies such as MPEG to appreciate that design of multi-channel encoders is a relevant topic.
Encoders capable of representing spatial audio information such as audio programme content by way of parametric descriptors are known. For example, in a published international PCT patent application no. PCT/IB2003/002858 (WO 2004/008805), encoding of a multi-channel audio signal including at least a first signal component (LF), a second signal component (LR) and a third signal component (RF) is described. This encoding utilizes a method comprising steps of:
(a) encoding the first and second signal components by using a first parametric encoder for generating a first encoded signal (L) and a first set of encoding parameters (P2);
(b) encoding the first encoded signal (L) and a further signal (R) by using a second parametric encoder for generating a second encoded signal (T) and a second set of encoding parameters (P1) wherein the further signal (R) is derived from at least the third signal component (RF); and(c) representing the multi-channel audio signal at least by a resulting encoded signal (T) derived from at least the second encoded signal (T), the first set of encoding parameters (P2) and the second set of encoding parameters (P1).
Parametric descriptions of audio signals have gained interest in recent years because it has been shown that transmitting quantized parameters describing audio signals requires relative little transmission capacity. These quantized parameters are capable of being received and processed in decoders to regenerate audio signals perceptually not significantly differing from their corresponding original audio signals.
A problem of significant inter-channel interference arises when output from contemporary multi-channel encoders is subsequently decoded. Such interference is especially noticeable in multi-channel encoders arranged to yield a good stereo image in association with two-channel down-mix. The present invention is arranged to at least partially address this problem, thereby enhancing the quality of corresponding decoded multi-channel audio.